This recirculation is generally carried out by means of a circuit referred to as EGR (Exhaust Gas Recirculation) circuit comprising a pipe connecting the engine exhaust manifold to the intake distributor thereof and a valve, referred to as EGR valve, arranged in this pipe.
As it is widely known, in order to be able to minimize NOx discharge into the atmosphere, this recirculated exhaust gas is generally cooled prior to being fed to the engine intake. A heat exchanger is therefore arranged on the pipe and the exhaust gas is cooled while flowing therethrough.
This EGR circuit layout is well known to the person skilled in the art and it is better known as “external EGR”.
What is also known, as described in document WO-2006/018,699, is an “internal EGR”, commonly referred to as “IGR” (Internal Gas Recirculation or Internal Gas Residual), which allows to reintroduce exhaust gas to the engine intake without using a specific external exhaust gas recirculation circuit.
The internal-combustion engine therefore comprises a cylinder provided with a combustion chamber, an exhaust means with an exhaust valve, an exhaust manifold, an intake means with an intake valve, an intake distributor and a recirculated exhaust gas cooling exchanger, or cooler, arranged in the intake distributor.
In this type of engine, the exhaust gas is reintroduced to the intake in order to be mixed with the fresh air flowing in during the engine intake phase.
Thus, during the engine exhaust phase during which the exhaust valve is open, the intake valve is also open for a predetermined time. The exhaust gas contained in the combustion chamber is discharged simultaneously to the exhaust manifold and to the intake distributor. In the example described, the intake valve closes before the end of the exhaust phase and advantageously before the exhaust valve closes. In the example illustrated by this document, the exhaust gas contained in the intake distributor is cooled by the cooler and kept in this distributor at the desired temperature.
During the engine intake phase, the intake valve opens again, substantially as the exhaust valve closes. The cooled exhaust gas contained in the distributor and the fresh air flowing in are fed, through the intake valve, into the engine combustion chamber for the rest of the combustion cycle.
This layout, although satisfactory, however involves some quite significant drawbacks.
In fact, introduction of the recirculated exhaust gas and of the fresh air into the combustion chamber does not allow to obtain homogeneous mixing of the two fluids. This has the effect of disturbing the combustion of the mixture upon fuel injection in the neighborhood of the end of the engine compression phase.
Furthermore, during circulation of the exhaust gas in the cooler, the latter fouls up through deposition of the particles carried by the gas. The cooler therefore loses its exchange capacity, thus decreasing the performance thereof.
Moreover, as the exhaust gas flows through the cooler, condensation of the steam present in this gas may occur; this steam is then reintroduced into the cylinder during the intake phase and it is likely to disturb the combustion of the fuel mixture.
Similarly, it is difficult to control the amount of exhaust gas flowing through the cooler and a quite significant amount of this gas may not be cooled.
The present invention aims to overcome the aforementioned drawbacks by means of a method for reintroducing exhaust gas to the intake of an internal-combustion engine of simple design.